This invention relates to froth flotation and, more particularly, to column froth flotation for beneficiating mineral ores and the like.
Froth flotation has been used to beneficiate a variety of mineral ores and to effect separation of various other materials for many years. Froth flotation involves the separation of particles from each other in a liquid pulp based on differences in hydrophobicity. The pulp is aerated by introducing a plurality of minute air bubbles into it. The air bubbles tend to attach to the floatable (hydrophobic) particles and cause those particles to rise to the surface as a froth product which overflows from the flotation device, leaving behind the non-floatable (hydrophilic) particles.
An article entitled "Flotation Machines" in Mining Magazine, January, 1982, page 35, describes several different types of flotation devices and processes used for beneficiating minerals. In so-called column flotation, a conditioned pulp is introduced into the midzone of a relatively tall column. pressurized air is introduced through a diffuser in the bottom of the column, and wash water is fed into the top of the column. A fraction containing the floatable particles, usually the mineral values, overflows from the top of the column and a fraction containing the non-floatable particles, usually the gangue, is discharged from the bottom of the column by gravity or a pump. Examples of prior column flotation devices and processes are described in Canadian Pat. Nos. 680,576 and 694,547, Canadian Chemical Processing, February, 1965, pages 55-58, and E & MJ, Volume 66 No. 1, pages 76-78, 83.
The air diffusers in flotation columns have a tendency to become plugged, particularly when a lime depressant is used causing an uneven distribution of air throughout the pulp. Also the small air bubbles generated at the bottom of the column tend to enlarge as they rise toward the top due to a change in static pressure within the column, resulting in a reduced surface contact between the air and particles. Several different approaches have been used to alleviate this problem, including the use of hydrophobic materials and, instead of using a diffuser, introducing the air as a fine dispersion in water. The latter approach is disclosed in U.S. Pat. No. 3,371,779.